Name: ..................................................... ASTRONOMY 1102 { 1 Instructor: Juhan Frank Second Test {FALL 1999{ Friday Octob er 15 Part I { Multiple Choice questions 3 pts/question; total = 60 pts Identify the correct answers by placing a checkbetween the brackets [ ]. Check ALL correct answers in the questions identi ed bya *. *1 Some are wrong; which are correct? [x] The sp ectra of stars have absorption lines. [ ] The sp ectra of all stars have emission lines in optical wavelengths. [x] The sp ectrum of a hot solid is a continuous sp ectrum. [ ] The color of a star dep ends on the star's luminosity. [x] The color of a star dep ends on the star's surface temp erature. 2 The absolute magnitude of a star is a measure of the star's [x] luminosity. [ ] surface temp erature. [ ] mass. [ ] apparent brightness. [ ] density. 3 The apparent magnitude of a star is a measure of the star's [ ] luminosity. [ ] surface temp erature. [ ] mass. [x] apparent brightness. [ ] density. 4 Sunsp ots lo ok darker than the photosphere b ecause [ ] they are hotter. [x] their temp erature is lower than 5800 K. [ ] the magnetic eld is weaker in the sp ots than in the surroundings. [ ] they are holes in the surface of the sun. [ ] all the energy is emitted as X-rays. 5 Given G Universal constant of gravity, the mass of the sun can b e measured using [ ] Stefan-Boltzmann's law. [ ] Wien's displacementlaw. [x] Kepler's third law as mo di ed by Newton. [ ] spring scales. [ ] a sp ectrograph. 6 The most correct equation representing the overall e ect of the pp chain is 4 [] 4 He ! H. 2 1 4 H ! He. [] 4 1 1 4 + [] 4 H ! He+2e . 1 1 4 + [x] 4 H ! He+2e +2 . 1 18 4 [] O ! 4 He. 8 A1 7 The sp ectrum of a p erfect thermal emitter of surface temp erature T lo oks like [x] a blackb o dy curve with the temp erature T without any lines. [ ] a pure emission line sp ectrum. [ ] a blackb o dy curve with the temp erature T with absorption lines. [ ] a blackb o dy curve with the temp erature T with emission lines. [ ] the sp ectrum of a low density gas at a temp erature T. 8 The total radiativepower p er unit surface emitted by a blackbody [ ] increases linearly with temp erature / T . [ ] decreases in inverse prop ortion to the temp erature / 1=T . 2 [ ] increases as the square of the temp erature / T . 4 [x] increases as the fourth p ower of the temp erature / T . [ ] do es not dep end on the temp erature. 9 In the sun, the correct order from the center outward: [ ] wind, chromosphere, core, convection zone, photosphere, radiation zone, corona. [ ] core, convection zone, radiation zone, photosphere, corona, chromosphere, wind. [ ] photosphere, chromosphere, corona, wind, core, convection zone, radiation zone. [ ] core, convection zone, radiation zone, photosphere, chromosphere, corona, wind. [x] core, radiation zone, convection zone, photosphere, chromosphere, corona, wind. 10 The solar energy is carried by blobs of gas rising and falling similar to b oiling in the [ ] core. [ ] solar wind. [] chromosphere. [x] convection zone. [ ] radiation zone. *11 The lower the frequency of electromagnetic radiation, [ ] the shorter its wavelength. [x] the longer its wavelength. [ ] the higher the energy of the photons. [x] the lower the energy of the photons. [ ] the slower it moves through space. 12 The numb er of solar neutrinos detected in terrestrial exp eriments is [ ] greater than the mo dels predict. [ ] consistent with the amount pro duced in the solar core. [x] less than the numb er that must b e pro duced bynuclear reactions in the core. [ ] almost zero b ecause they have all converted to undetectable typ es of neutrino. [ ] exactly zero since no neutrinos are pro duced by the pp chain. 13 The distance to a star having a parallax of 0.25 arcsec is [ ] 0.25 p c. [] 4LY. [] 4". [ ] 2.5 p c. [x] 4 p c. A2 14 All stars found on the Main Sequence are [x] burning H to He. [ ] burning H to He by the pp chain. [ ] burning H to He by the CNO cycle. [ ] burning H to He at the same rate as the sun. [ ] burning H to He at higher rates than the sun. 15 A yellow G2 sup ergiant has [ ] a higher luminosity, larger radius and higher surface temp erature than the sun. [ ] a higher luminosity, smaller radius and higher surface temp erature than the sun. [] alower luminosity, the same radius and lower surface temp erature than the sun. [x] a higher luminosity, larger radius and the same surface temp erature as the sun. [ ] a higher luminosity, larger radius and lower surface temp erature than the sun. 16 Jupiter is approximately 5 AU from the sun. The solar ux measured on Jupiter is [ ] 25 times the solar constant. [ ] 5 times the solar constant. [ ] equal to the solar constant. 1 of the solar constant. [] 5 1 [x] of the solar constant. 25 17 A B3V star app ears white blue b ecause it [ ] only emits white blue light. [x] emits electromagnetic radiation of all wavelengths but more blue than red. [ ] emits no red light. [ ] emits more blue light than UV. [ ] absorbs almost all red light, so more blue is left over. 18 The Earth's atmosphere is transparent in the following \windows" [x] optical and radio. [ ] optical and X-rays. [ ] far infrared and short wavelength UV. [ ] X-rays and radio. [ ] optical and far infrared. *19 The largest and the smallest of the stars having the following sp ectral typ es [ ] O3V. [ ] M6III. [ ] A2V. [x] M5V. [x] K2I. *20 The co olest and the hottest of the stars having the following sp ectral typ es [x] O3V. [x] M6I I I. [ ] A2V. [ ] M5V. [ ] K2I. A3 Part I I { Problems 10 pts/problem; total = 40 pts NO CALCULATORS! Problem 1: More Powers of Ten: The total mass of hydrogen available for fusion into Heli- 29 um in the sun is approximately 2 10 kg. The current rate of burning is approximately 600 billion kg/s. One year is equivalent to 31.5 million seconds. Estimate the lifetime of the sun in years. The lifetime in seconds is: 29 2 10 kg 2 1 2911 18 t = = 10 s= 10 s Life 2 9 6 10 10 kg =s 6 3 Converting to years: 18 18 10 yr 10 s 10 = =10 yr t = Life 7 8 3 3:15 10 s=yr 10 Problem 2: Two stars in a certain CCD exp osure taken by the Hubble Space Telescop e are of very di erent brightnesses: star A has a magnitude 7, while star B has a magnitude of 22. a Which of the two stars is brighter? The star with the SMALLEST apparent magnitude appears brightest: Star A. b What is the ratio of uxes of the brighter star to the fainter star? The di erence in magnitudes is 22 7=15. Every 5 magnitudes is equivalent to a 6 ux FACTOR of 100. So 15 magnitudes correspond s to 100 100 100 = 10 . A4 Problem 3: A distant galaxy shows an emission line whose rest wavelength is 400 nm shifted to 480 nm. Is this a blueshift or a redshift? Is this galaxy moving toward us or away from us? At what sp eed is it moving? Since > this is a shift to LONGER wavelenghts or a REDSHIFT. So the obs rest galaxy is moving away from us. The shift is = =80 nm. The Doppler obs rest formula then gives us the speedas 80 v = = =0:2 c 400 rest So the speedis0:2c or 60,000 km/s. Problem 4: The diagram b elow shows a hot O3V star, which emits by de nition \an O3V sp ectrum", and a cloud of gaseous Hydrogen and Oxygen at a lower temp erature than the star. Several lines of sight are drawn with the \eye" indicating the p oint of view, and lab elled with numb ers. Write in the space provided the typ e of sp ectrum you should see from each of the chosen vantage p oints. If emission or absorption lines are seen identify which elements pro duce them, so for example, you could say \an O3V sp ectrum with additional H and O absorption lines", or \an O3V sp ectrum", or "an emission sp ectrum of ...such and such element...". See Figure 1.{ Emission spectrum of H and O. 2.{ O3V spectrum. 3.{ Emission spectrum of H and O. 4.{ Emission spectrum of H and O. 5.{ O3V spectrum with additional H and O absorption lines. 6.{ Same as 5. A5.